SEOUL – The pro-American conservative presidential candidate got a much-needed boost in the form of an endorsement from the leading minority candidate but has obstacles to overcome before the election next Wednesday.

A mood of optimism pervades rallies of Yoon Suk-yeol’s People Power Party here and around the country going into the final weekend of a bitterly fought race against Lee Jae-myung, candidate of the ruling Minjoo (Democratic) Party. In the final polls before the start of advance voting on Friday, Mr. Yoon led by anywhere from 1 to 6 percent.

Mr. Yoon displayed his hard-line position vis-a-vis North Korea by visiting the United Nations Memorial Cemetery in Busan, the sprawling southeastern port city that is a stronghold for conservatives, as early voting began. It is necessary, he said after casting his ballot, “to change the government and find new hope” — a reminder that he had resigned as prosecutor-general last year after finding corruption among top officials in the government of President Moon Jae-in.

Mr. Lee, voting in Seoul, said if elected he would “open the path of unity, economy, and peace,” a reference to his confidence in dialogue as the way to reconciliation with North Korea amid economic problems at home.

Mr. Yoon counted on the endorsement given by Ahn Cheol-soo, a wealthy entrepreneur seen as a political moderate, to give him the edge. At a joint press conference, they issued a statement anticipating “a perfect change of government” as a result of the merger of their campaigns. Mr. Ahn, who had been polling at between 5 and 10 percent, was assumed to have reached a deal for a cabinet seat. There was even talk that Mr. Yoon, if he wins, might make Mr. Ahn his prime minister — an appointive position.

Campaign workers wearing red jackets for Mr. Yoon and blue for Mr. Lee proselytized on street corners, reminding everyone the poll numbers could fluctuate before election day.

At a rally I attended in central Seoul, a red-jacketed advocate for Mr. Yoon seemed sure his candidate would win but warned against swings or surges as seen in wavering poll numbers in recent weeks. “We cannot be overconfident,” he said as campaign workers shouted slogans. “We need to make sure people care enough to vote.”

In Mr. Lee’s camp, the mood was one of disappointment five years after “the candlelight revolution” precipitated the impeachment and jailing of the previous conservative president, Park Geun-hye, daughter of a long-ruling dictator, Park Chung-hee, who was assassinated by his intelligence chief in 1979. “We must revive the spirit of our revolution,” said an aide to Mr. Lee, recalling the time in 2016-17 when hundreds of thousands of people turned out nightly here carrying LED candles calling for Ms. Park’s ouster and prosecution on multiple charges of corruption.

The revolution preceded the election of Moon Jae-in as president by an easy majority over the conservative candidate. Mr. Moon, however, has come under intense criticism for economic difficulties in which middle-class and poor citizens have seen their buying power diminish even as the economy grew. He has also been the target of criticism for wanting to appease North Korea’s leader, Kim Jong-un, who has not responded to his calls for dialog.

Mr. Moon, who by law cannot run for a second five-year term, has pursued  a soft-line policy toward the North while remaining neutral on many issues involving Russia and China.

His pleas for an “end-of-war declaration” in which North and South Korea and China as well as America would affirm that the Korean War, which ended in a truce in 1953, is really over have aroused no interest in Pyongyang or Beijing. In Washington, U.S. officials fear the declaration would lead to negotiations for a peace treaty in which North Korea would simply reiterate demands for an end to the historic alliance with South Korea and withdrawal of America’s 28,500 troops from the South.

Mr. Moon, also criticized for having initially expressed only “regret” over Russia’s invasion of Ukraine, adopted a tougher line in a telephone conversation with President Zelensky. After chatting for half an hour, he tweeted that Korea “expresses its respect to President Zelensky for his strong leadership” and stands “in solidarity with the people of Ukraine who have risen resolutely to defend their country.”

Still, the tweet did not mention President Putin by name or hold him responsible for violating the sovereignty of a democratic nation, much less accuse him of war crimes. They did show Seoul’s desire to line up with Washington and its NATO allies. South Korea is supporting sanctions against Russia after having appeared hesitant a week ago.

Mr. Moon has sought to show the quality of mercy by pardoning the former president, Park Geun-hye, freeing her from a lengthy prison term. Hospitalized for muscular and joint problems, she has said she would live in her native Daegu, a bastion of conservative power in southeastern Korea.